Modernizing the compute servers model

* Added server list models
* Fixed issue where some server properties were not being
  populated when deserialized from xml
* Fixed issue where task_state was different between
  JSON and XML when the value was 'none' and
  updated relevant test
* Added States for task_state
* Set all properties for server models explicitly
* Modified servers client to use new server list models

Change-Id: I61307e457e08d106e10ff5a16563d9b4f5171daf
Merge "Modernizing the compute servers model"